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De-watering Boston Whaler Boat Hulls by Vacuum Bagging
|Author||Topic: De-watering Boston Whaler Boat Hulls by Vacuum Bagging|
posted 09-28-2010 12:46 PM ET (US)
I am in the process of picking up a used 17 that has seen better days. From what I can see the hull is pretty wet and I would like to dry it out. I have the required equipment to vacuum bag the hull in an attenpt to remove the water from the foam.
My plan is to use a hole saw to make some relief holes and bag over that area so that the vapor has a place to pull to. I will use the spiral vent hose to create an path for the vapor to escape.
Has anyone tried this or something similiar? Please don't post and tell me not to worry about it as that appears to be the standard response.
posted 09-28-2010 01:02 PM ET (US)
You might check out boardlady.com. This woman builds and repairs sailboards and commonly uses vacuum bagging techniques in her repairs and gives some good advice on her site.--Paul
posted 09-28-2010 01:09 PM ET (US)
I bagged my 22 Outage with a dehumidifier for some time to try and draw out moisture of the exposed foam around the fuel tank. It did virtually nothing. Many have tried to dry hulls out using all kinds of ways with little to no success.
I hate to say it but the only way to get dry foam in your hull is to cut out the wet foam and refoam.
posted 09-28-2010 01:34 PM ET (US)
I don't know how many Boston Whaler boats the woman who runs the surfboard website has successfully de-watered. If she can do it, it would be quite interesting to find out. My guess is that Jeff's experience might be more cogent to this inquiry.
posted 09-28-2010 04:37 PM ET (US)
[T]hanks for the link. [The process described for drawing water from surfboards] is very close to what I would like to do.
I did read [Jeff's] post on the bag and dehumidifier trick and this is much different. Using a dehumidifier will ensure the air near the boat is dry, but, will not actually draw any water out. The vaccuum will actually such the water out of the pores of the foam under presure.
posted 09-28-2010 04:51 PM ET (US)
I'm not going to tell you not to worry about a water logged Boston Whaler hull, but I will tell you that your method is not going to remove more than a few cups of water.
posted 09-28-2010 05:01 PM ET (US)
Sam--Give the vacuum bagging technique a try and please let us know the results. In order for CONTINUOUSWAVE to accumulate information about Boston Whaler boats, people have to contribute information about Boston Whaler boats. I don't know that the technique of vacuum bagging has been exhaustively tried by anyone and the field of vacuum bagging (as a way to de-water a Boston Whaler boat hull) completely explored.
Since you already know how to use vacuum bagging and apparently have all the equipment to perform vacuum bagging, I am not sure you need to be schooled in vacuum bagging. I am not sure that the technique used on a surfboard where the foam is probably only a few inches deep will be immediately applicable to a Boston Whaler where the foam might be a foot deep in places. To me, you sound like you are ready to go with vacuum bagging. So, please go to it, and see what happens to that soggy foam.
I wish you success, and I hope it works. There are many folks with older Boston Whaler boats with some water in the hull interior that would like to know of a good method to remove the water.
If you report back on the results, then we'll have some information about using vacuum bagging to de-water the foam in a Boston Whaler, right here on CONTINUOUSWAVE.
posted 09-28-2010 05:13 PM ET (US)
It would be interesting to see the results. A vacuum bag is very different than a humidifier in how it would dry. The vacuum bag could effectively result in the water "boiling" at room temperature.
The main question I would have on it working is I don't have a feel for how air permeable the foam is - if there is not decent air permeability it would only dry the edges. But for water to suck into the foam the foam must have some air permeability.
posted 09-28-2010 05:35 PM ET (US)
I'm not the first to say this, but anywhere water can get, air can get... and so the vacuum must work to some extent. Whether this is worth the time, energy, or how many holes it will need is another story- only one way to find out!
posted 09-28-2010 06:52 PM ET (US)
Vacuum bagging to boil water to vapor and sucking out the vapor is possible. At my work we use this method almost daily but instead of a bag we use a 3' X 5' vacuum chamber. While the vacuum to boil water is quite high the entire boat would have to be sealed to pull the vacuum necessary. After the vacuum is pulled it would suck the foam flat and quite possibly suck the structure of the boat flat inside the bag long before the water started to boil. You can lower the boiling point by raising the temperature of the boat and then it would still take a fair amount of vacuum to finish out the vaporization process but it would still collapse the foam. We vacuum boil water from 30% moisture to under 1% in our process.
posted 09-28-2010 07:07 PM ET (US)
I have yet to see or hear of a way to get the water out of a whaler hull with any kind of success. Other than ripping the hull apart a taking out the bad foam, and re-glassing it, I think you will be doing more work that getting the results you will be looking for. Depending on how much the hull weighs (determine how much water is in the hull) you my be better off looking for a better hull....Good luck on you endeavor
posted 09-28-2010 10:11 PM ET (US)
Sam--If you try it, your idea regarding drilling some vent holes to allow air to enter makes sense. I'd drill the holes at the "far" end and tilt the rig so some gravity can assist. For example, drilling along the bow section, where the seam between the upper and lower hulls are glued together. Place the vac line at the stern, low with the hull tilted as much as possible. Can you rig a water trap to measure how much is eliminated?
Regards - Don
posted 09-29-2010 07:46 AM ET (US)
If I am correct there are a number of plywood stingers running athwartship in teh hull with foam poured b etween each one. Does anyone know the spaciong of these members as I will need to put a bleed hole in each chamber to get good suction.
posted 09-29-2010 11:14 AM ET (US)
In an issue of Professional Boatbuilder (#126) there is an article on using vacuum to dewater the core of a large (very large compared to Boston Whalers) sailing vessel. This boat was built using a kerfed PVC foam core (Divinycell) sandwiched between layers of resin and kevlar/glass. Although not directly comparable to a Boston Whaler, the article includes some interesting information on various methods of producing a suitable vacuum for the drying process. I have the print version of the article but it may be possible to locate it at:
The bottom line is that even in a very thin foam core it takes a great deal of vacuum to dewater the foam. They used a regenerative vacuum generator along with dry compressed air to dry it a small section at a time.
I'm not suggesting it can't be done (and as I own several older Whalers and may be in the position of needing to do this myself someday I hope it CAN be readily accomplished), just giving some pointers to information. Good luck Sam!
posted 09-29-2010 12:28 PM ET (US)
You are not correct.
posted 09-29-2010 04:09 PM ET (US)
Well I bought it. We'll see where she goes from here.
Back issue of Pro Boat is on the way.
posted 09-29-2010 04:19 PM ET (US)
I'm surprised that I'm the first to post the reference to Chain Saw Whaler, but it should make some very interesting reading for you. Obviously it's an extreme case, but it makes the probability of success for drying out a hull look pretty poor.
posted 09-29-2010 11:44 PM ET (US)
I like the way you run and moderate this site... really. I mean it. With that said... <insert wrinkled brow here>... I see a few replies from you to a few things here that make me think you got up on the wrong side of the bed. Rather than saying "You are Wrong", why not welcome a member and help the guy out with some information?
It's your site and all, but... sheesh.
posted 09-30-2010 08:20 AM ET (US)
Thanks for your thoughts, but, I got the answer I was looking for in clear concise fashion. I'm good with that.
I took a couple of core samples in areas where I thougth the deck was wet and it is. Next step is to seal the bottom crack so I can pull a vaccuum fromt he top deck. it shoudl get prepped later this week so I can suck on it during the days next week.
posted 09-30-2010 08:58 AM ET (US)
Dave--Thank you for the kind words you have expressed about the website.
For more information on the construction technique of the Boston Whaler Unibond hull, see
posted 09-30-2010 10:27 AM ET (US)
Sam- please take pictures of this project if possible... we would be interested in following your progress.
posted 09-30-2010 10:52 AM ET (US)
I will try and take lots of pics and provide documentation. It appears that this is not a process without precedent so I am please to know I am on a track that other have succeeded along. The most unfortunate thing is that I don't think that I will be able to get a before weight as I do not think I have an appropriate scale at my disposal. I know what the target weight is so I will have to shoot for that.
|Tom W Clark||
posted 09-30-2010 11:20 AM ET (US)
You are not going to be able to suck any significant mount of water out of your hull. Been there, done that. The foam core of the Whaler UniBond hull holds water quite tenaciously. It will not drain, out, it will not be "pulled" out by vacuum.
It will dry out given time, but the time needed is years, perhaps decades.
You may want to read a bit about the waterlogged hull I had experimented with, Chain Saw Whaler discussed extensively in this three piece thread:
My experimentation with a vacuum pump is discussed in part Two:
The vacuum canister is shown in these photos:
There is also good documentation of drying a Whaler hull over time with Jim Potdevin's waterlogged Squall, shown in Cetacea Page 67:
...and discussed here:
The most intriguing idea for drying a Waterlogged hull was proposed years ago by Bruce Montgomery. He suggested using an old steel shipping container that could be sealed and then using a vacuum pump to lower the boiling point of water thus turning the water on the hull to vapor. Heat and high altitude would help, but I am still not sure this vacuum chamber would not destroy the foam in the process.
posted 09-30-2010 12:22 PM ET (US)
I did read your post as well as other who felt they were more successful than you were. Your thread is very informative and I have gone over it very carefully, however, a small medical grade vacuum pump pulling through a suction cup is akin to putting a 12V trolling motor on a 17' and declaring it a displacement hull based on the fact you couldn't put it on plane.
For starters the equipment I will be using is sufficient for infusing parts roughly the size of a 13' whaler. That requires higher pressures and volumes that I expect that you saw. If the pump you were working with had sufficient capacity to pull a vacuum then you would have had to bag the whole hull or seal any and all penetrations in the skin so that there was no air leaking in.
While I might not have the time and resources to actually pull this off this method or something similar should work well. I say this with certainly knowing that the water moves through the cell structure of the foam as we know. The water gets there by
A) gravity water on deck falling seeping from above through broken fittings, screw holes, etc...
B) water pressure exerted by the hull on top of the water pushing it up through fractures in the fiberglass skin or exposed glass where gel coat has been scratched off
The technique espoused often as the most effective is to drill holes and drain the boat over a long period of time. This again relies on gravity as the force to remove the water. Pulling a vacuum of ~30psi will significantly increase that force and SHOULD move the water much faster as a gas or liquid. Again we are talking hypotheticals here so I will need to prove this out.
posted 09-30-2010 02:33 PM ET (US)
As Tom mentioned my 1968 Squall. The original weight is published as 125 lbs. The Squall has been sitting on her transom for 7 of the last 8 years.
Bow Stern Total Loss
Hope this table makes it in one piece.
posted 09-30-2010 03:15 PM ET (US)
Jim: seems like the boat is averaging 24.7 lbs of water a year. Starting at #484 and down to #247 with only another 112 lbs. left. I guess there is only about 4.5 more years to go. Good thing no one is in a hurry. (9 ft Whaler Squall 15 year restore project)
posted 09-30-2010 03:44 PM ET (US)
I would save a little more money and buy a buy a dry hull to begin with. I am in the process of refinishing a 74 montauk and the time and money you spend will be worth far more than what you would have to spend to get an equivalent boat when you are done.
posted 10-01-2010 02:11 PM ET (US)
To pull a vacuum you have to have more suction than air that is leaking in. Pulling a vacuum down to 30 inches means you have an absence of intrusion of anything whether it be air, gas or liquids. If you’re planning to use suction to remove water and replace it with air you are not creating a vacuum at least not to a significant amount. One issue you will have is creating suction at point a and leaking dry air in from point b will only help until you create a point of least resistance and then either you collapsed foam cells or delaminated the foam from the glass at that point suction that would remove water is replaced by air movement. In my work we use liquid ring vacuum pumps and pull to about 29.5 inches on a sealed chamber to dry moisture laden fiberglass before we coat it. We lower the vapor pressure and boil the moisture out at room temperature. We pull this load on raw glass fabric at 800 lbs of material at a time and from room storage at close to 30% moisture down to less than 1% moisture in 12 hours. This is very expensive to do to maintain a vacuum on boiling water. It takes an 8 cubic foot a minute 1/2 hp 3 phase vacuum pump to accomplish this task. We do this 2-3 times a week for the last 12 years. Judicious use of suction will help you to remove water but pulling a vacuum to boil it out is a whole other animal. Just be careful as high vacuum levels can do allot of damage.
Have fun in your adventure.
posted 10-01-2010 04:50 PM ET (US)
Sam - you have probably already thought about the placement of the holes - and the fact that any fluid flow always take the path of least resistance - which, in part says, limit the number of holes.
And for everyone, there has been much discussion regarding boiling off the water - but this takes a very high vacuum (very low pressure) - for example, to boil at 70F requires a pressure of about 0.36 psia - which basically means NO leaks. And this sounds difficult, but possible - BUT THINK about the physical load on the hull. That is, that low of a pressure on the foam means that the crushing load on the hull will be about 14.3 psi - pounds of force per sq inch - and there ARE A LOT of square inches. Be assured that the BW designers did not consider this crushing load in their design. --- Jerry/Idaho
posted 10-04-2010 01:13 AM ET (US)
Do note that JimP is in Alaska, and I'd presume the Squall is
to. I've wondered for some time how fast whaler foam would
dry parked in the summer sun in Yuma, or Death Valley, or
posted 10-04-2010 04:55 AM ET (US)
A good result is possible by applying heat.
The way to do this is using a heat cabin which is normaly used in the car bodyshops.
A member of our whalerclub has tried to repair his (our old) 17 Outrage after it broke loose from its mooring place in Kroatia and has been pounded on the rocks all night in a storm. The hull had several big gaps and collected water.
When the boat was all fixed and painted, it went into the cabin.
All repaired patches came out and were blowing steam, prooving that this is a way to get the water out.
The repair needs to be done over, but we think this is a possible way to succes.
I keep you posted on the end result.
posted 10-04-2010 12:30 PM ET (US)
I have never used expanding foam but heard that the chemical reaction puts out a LOT of heat. Not sure how easy it would be, but could the OP cut out sample/vent holes and refill with new foam, heating the surrounding areas and evaporating the water?
posted 10-04-2010 02:29 PM ET (US)
This may have no application here, but I throw out what I found as a facinating procedure during the construction of my vacation home in N. Idaho. As part of the design, I used a number of wood beams that were around 8" by 8" and 30 feet long. Getting the moisture level even throughout the beam is important to prevent cracking during the life of the intended use. My builder used a company in Oregon who places the beams in a vacuum chamber, pulls a vacuum and hits it with microwaves. I do not know the details, but the way it was explained to me, it is a low temperature, non-destructive way to quickly remove water from the wood that is consistent across the beam. If water can be removed from an 8X8 beam, I assume it can be removed from foam. Please, no flames or attacks, as I am not an expert. I only know that 6 years later, the beams are completely crack-free and remain as they were on day one.
posted 10-04-2010 06:30 PM ET (US)
That is fascinating on how they dried the beams sure reeked havoc on any termites that may have been hiding. 30 foot microwave auto clave must be pretty impressive. That is one heck of a hunk of machinery.
posted 06-22-2012 06:46 AM ET (US)
Any news concerning Sam's trials to dry the hull ? I've the same issue with my 16' SL and I'm looking for a solution ...
posted 06-22-2012 01:15 PM ET (US)
I wonder if a centrifuge would work? Poke some small holes at the ends and spin the boat for several hours. Maybe the force would be enough to get the moisture to propagate to the holes and fling out? A generic centrifuge wouldn't be that expensive (relative a big vacuum chamber) to build. A shaft, some cables and a counterweight and a motor. What do you think?
If the entire boat is vacuumed in a chamber, I imagine the vacuum would need to be increased very gradually. If a lot of water boils all at once then it might poof the boat up like a balloon. Ever see a marshmallow in a vacuum chamber?
posted 06-23-2012 03:20 PM ET (US)
A small comment to your post on the causes of water intrusion. The gel coat does not keep the water out. The resin that bonds with the roving keeps the water out. Boats do not need to be gel coated to function.
posted 06-25-2012 01:43 AM ET (US)
I don't get it. Why don't you just saw the deck off, cut out the old foam, reattach the deck using normal fiberglass repair procedures, cut some relief holes and inject foam? Seems like you'd be done and fishing instead of watching a vacuum gage and getting older. Sometimes simpler is better.
I had a waterlogged flying bridge deck on a 42 footer (about 10'w x14'L) and I just used my skill saw to cut and remove the deck in several pieces. I replaced the wood and glassed the decking back in place. Then I faired and painted the decking and non skid. the boat was down for less than two weeks including painting. You'd never see the seams even if I showed you where they were.
posted 06-25-2012 12:32 PM ET (US)
What is the point? Its not that any Whaler is a rare model. Sell it for what you can get and buy a dry one. The simple way is always the best way.
posted 06-28-2012 09:18 AM ET (US)
I'm confused by the theory that pulling a vacuum will remove water from the hull of a Boston Whaler. If there is a vacuum then there is no air flow, which is exactly what is needed to dry out anything.
I would attach the vacuum at the lowest point available on the hull but leave averything else as is, allowing air to enter the hull at all the water intrusion points.
In either case the air will follow the path of least resistance, which may not be where the wet foam is located.
This all just theory of course and only my 2 cents worth.
posted 06-28-2012 02:43 PM ET (US)
@Bthom, if you pull enough vacuum then water will boil at room temperature. The idea is to boil off the water. This is a common method for drying out closed systems, such as your air conditioner before it is filled with refrigerant. The challenge is that you need to pull a reasonably high vacuum.
posted 06-28-2012 09:56 PM ET (US)
Yes, I understand the whole pressure vs boiling point thing but as soon as the pressure rises the water vapor will condense back into liquid form.
I guess the theory is that the expansion of the water vapor during phase change will force some of it out of the hull, leaving less in the hull to condense when the pressure is raised back to atmospheric?
In order to get water to boil at 79.6 degrees you will need to reduce the pressure to 0.5 psi, which is next to impossible without a facility designed and built specifically for that purpose.
posted 06-29-2012 10:04 AM ET (US)
The water does not have to boil to evaporate. Pulling a vacuum reduces the moisture content of the air in the chamber. The air removed during the process contains moisture thus the air left behind will have less moisture for it's volume, or reduced humidity.
Water evaporates more quickly when humidity is lower.
Adding heat is an easier way to accomplish the same thing. To reduce the moisture in a boat bag it tightly in black plastic sheeting and leave it out in the summer sunshine. If the "bag" is tented carefully the water that condenses on the inside of the bag will run down to the bottom of the bag. At the end of the day the bag can be opened, drained and closed again. Repeating the draining process for several days will remove much of, or all, the moisture exposed to the heated air.
The problem is not to create a heating or vacuum chamber but to expose the moisture to the ambient air within the chamber.
posted 06-29-2012 11:08 AM ET (US)
Guys, I have been watching this post for a while and there are many opinions and here is mine. It takes 2 things for water to evaporate- heat and air. Heat is present in anything above absolute zero which is not achievable, so air is the most critical. Elevated heat does help, but water will evaporate at any temperature humans operate in if exposed to air.
Take that salmon in the freezer. If air gets to it, you have freezer burn which is simply the fish drying out on the surface. It dries on the surface, but the moisture frozen in the center does not dry because it is protected from the air.
This is similar to the closed cell foam in a Whaler. The water which soaks in over a long period of time cannot get to the surface to be exposed to air and the air cannot get into the foam where the water is trapped. Thus, drying limited to a small area. The water did not soak in in a short period and it will not dry in a short period.
IMHO, it is possible to dry small areas, say inches, from an opening, but can take years to dry an area measured in feet. The water and air are just not going to migrate in closed cell foam.
Bagging and vacuum may help, but minimally and again, in small areas. The time drying will take is clear in the experiment listed earlier in the post - years.
Conversely, a wet transom will dry out over time if exposed to air. It is made of wood, and water will migrate in wood. It can still take weeks or months, but not years like closed cell foam.
posted 06-29-2012 03:35 PM ET (US)
Good point jfortson, like I said I have NEVER heard of anyone using any method to get water out of a whaler unless they open the glass and replace the foam period
posted 06-30-2012 07:51 PM ET (US)
From my experience, you can salvage a wet boat. in 2007 I purchased an 11' standard that had been left in salt water for a couple of seasons. Frozen in solid and thawed several times. No photos, but it only had an inch or two of clear freeboard when I bought it. Four adults could not budge it. That was with no motor.
When I launched it in spring 08 it rode very nicely.
Over that winter it was under cover,and a fan circulated air on nice days. Various vacuum pump and compressed air schemes were tried, but none produced any large amounts of water. Bagging was not tried. Several repairs were necessary , maybe 20 square inches of foam were exposed, some water drained from these. I'm sure it wasn't dry, I'm sure it was overweight, but it was quite usable when completed. I believe patience and good airflow on warm low humidity days did most of the work. I should have documented the process better.
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